Hydraulic pistons have provided a simple and inexpensive means for lifting loads, but existing systems incorporate valves with small needle orifices that can become blocked or partially blocked with foreign particles in the oil resulting in restriction in normal oil flow in the control section of the valve. This can cause elevator travel while the doors are open. The electric control circuit shows the elevator has stopped but the mechanics of the valve (control oil system) have not performed properly and in actuality the elevator has not stopped, it continues to travel with doors open.
Present systems that include valves also have temperature, pressure and viscosity oil problems.